Learn the Difference Between the Bots and Live Players
In solo play many of the opponents are bots. They usually are weeded out by the time you get to 5 or less players (though sometimes I've seen them make it to the number 2 position which astounds me).
Bots are very easy to kill once you get a feel for them. They have a couple advantages live players don't have, like they'll see you even if you are hiding in a bush, and will sometimes just know where you are and rush you, but generally they are free loot.
Just don't stay still when fighting them. They don't lead shots. They'll either stop and shoot at you and make themselves very easy targets, or slowly sidestep to the left or right.
If you mistake a live player for a bot, you are going to regret it.
An easy tell is that bots do not look around. They pick a path and just follow it for awhile. Real players look around and are generally paranoid.
Oh. Bots don't drive cars (I'm pretty sure of this). So thats also an easy tell.